Powder coating systems

ABSTRACT

A powder coating system is provided comprising a powder spray booth ( 2 ) with a powder recovery system having an overspray intake ( 18 ) communicating with the interior of the booth. A diverter plate ( 26 ) may be held within the booth ( 2 ) to define with the booth floor ( 10 ), a duct leading to an overspray intake ( 18 ) of the powder recovery system. The diverter plate may include apertures for allowing oversprayed powder to be collected through the plate. The diverter plate may be provided as two or more diverter plates held at different elevation levels within the booth to define a duct which is larger in parts of the duct which are closer to the overspray intake than parts of the duct which are farther from the overspray intake. Alternatively or additionally, the coating system may include an air assist which provides jets of air across a portion of the interior surface of the booth. The surface may be one or more sloped portions ( 22 ) of the floor. The air supply may be pulsed to produce periodic bursts of air across the interior surface.

[0001] This invention relates to powder spray coating and, inparticular, to the recovery of powder which has not adhered to thearticle to be coated from a powder spray booth.

[0002] The powder which does not adhere to an article to be coated in apowder spray booth is known as the “overspray”. Overspray powder maymiss the article to be coated, rebound from a surface of the article, orbe deflected by the electrostatic fields in the spray booth away fromthe article.

[0003] It is known to recover overspray powder by exhausting the airfrom the booth and hence the air-borne overspray powder. The filterelements which have been used to recover overspray from powder spraybooth are capable of removing substantially all the overspray from thespray booth exhaust air so that the powder may be reused. It is alsoknown to use cyclone separators instead of, or in conjunction withfilter elements for recovery of overspray. Cyclone separators areeffective in removing the majority of the overspray from the spray boothexhaust air and are easier to clean than filters because very littlepowder is deposited inside the cyclone housing.

[0004] In known arrangements the cyclone separators have been connectedto the powder spray booth by a duct extending from an overspray intakenear the floor of the booth to the inlet of the or each cyclone.European Patent Application No. 94929600.8 discloses a powder coatingsystem where the duct is built into the powder spray booth, with one ofthe side or end walls of the booth forming part of the duct.

[0005] In European Patent Application 98940476.9 there is disclosed afurther development wherein the portion of the side or end wall whichforms part of the duct is removable from the remainder of the wall toallow easy cleaning of the duct. That Application also discloses asystem for collecting deposited overspray powder comprising a scraperbar which continuously reciprocates across the booth floor between theend walls to collect powder on the booth floor and move the collectedpowder towards the end walls of the spray booth adjacent to each ofwhich overspray intakes are provided.

[0006] In recent years there has been a growing desire to be able tospray multiple colours in a single booth in rapid succession. However,changing powder colour requires cleaning of the booth to remove powderdeposited on the walls, ceiling and floor which was not extracted by airexhaustion. Proper cleaning of the walls and floor of the powder spraybooth between colour changes is very important to ensure acceptableproduction quality. Such cleaning may be carried out manually by anoperator using a scraping and/or compressed air jet apparatus. Howeverbooths have been proposed which are intended to automate the depositedoverspray powder cleaning process including the booth of European PatentApplication No. 98940476.9 referred to above with its reciprocatingscraper bar.

[0007] Whilst many developments have been made, there is a customerdriven demand for even more rapid cleaning capability to reduce cleaningtime still further. Furthermore, whilst automatic mechanical devicessuch as the reciprocating scraper bar of European Patent Application98940476.9 do accelerate the cleaning process, they also increaseconstruction cost and can be vulnerable to mechanical failure.

[0008] Cleaning is preferably conducted from one end of the booth toanother and so, from the point of view of cleaning, the overspray intakeof the powder recovery system would ideally be located at one end of thebooth. However, from the point of view of spraying, the best locationfor the overspray intake is commonly held to be in the lengthwise centreof the booth to give balanced extraction air flow along the booth andtherefore even air flow across the openings which are provided for thespray devices. When the overspray intake is provided at one end of thebooth, attempts have therefore been made to modify the boothcross-section to produce the desirable air flow balance. In one knownsystem the booth floor has side portions which slope downwards and theregion therebetween is vertically offset to define a trough between thesloped side portions. A triangular insert is positioned in the troughduring spraying. The combination of the sloped side portions andtriangular insert helps balance the air flows along the length of thebooth. However difficulties arise when the powder colour is to bechanged as the triangular insert has to be removed for cleaning whichadds to the cleaning time.

[0009] In another arrangement, shown, for example, in U.S. Pat. No.4,715,314, the booth floor is formed with a slot which extends thelength thereof and connects to a duct also running the length of thebooth. However the slot can accumulate powder when one colour is sprayedfor a long period of time which makes cleaning more difficult.

[0010] It is also been proposed to reduce cleaning time by preventingpowder from ever depositing on the floor of a spray booth. German Patent3408014 describes a system where the floor of the booth is formed as aseries of descending steps and air is blown across each step from theslot between it and the step thereabove. The aim is to provide an airstream across the width of the booth which will carry all powder fallingtowards the floor into the overspray intake and prevent the powderreaching the floor and depositing there. The step form of the boothfloor however increases the overall complexity of the booth and this,and the fact that air has to be continuously supplied, makes the boothexpensive.

[0011] German Patent Application No. 19644360 describes a booth which isalso intended to prevent overspray powder reaching the floor. The boothhas one or more nozzles for creating a generally horizontal airflowacross the booth floor. The air flow diverts descending overspray powdertowards the inlet of a powder recovery system and prevents the overspraypowder from depositing on the floor. In one embodiment, a central bafflepositioned above the floor creates an open-sided duct leading to theinlet and a nozzle directs air to each side. As with the system ofGerman Patent 3468014 a continuous air supply is required.

[0012] As noted above, booths in which part of the floor is sloped areknown. However, according to U.S. Pat. No. 3,905,785, sloping alone isinsufficient to cause all the overspray powder to flow by gravity to therecovery system. The Patent proposes a booth in which the floor isconstituted by at least one air-permeable inclined plate. Air is suckedfrom the booth through the plate which acts to filter out air borneoverspray. Periodically air is blown up through the plate to fluidisethe deposited overspray thereon and cause it to flow to a recoverysystem. The suction period may be five to twenty times longer than theblowing period. The concept is similar to that of cartridge filterswhich are periodically purged by reverse air jets.

[0013] The majority of known booths are rectangular. However, it is alsoknown to provide circular booths. A circular booth is disclosed in, forexample, EPA 0839522. A problem with known circular booths is that thesehave conical floors leading to a suction duct by which overspray powderis transferred to a recovery system. A pit is generally required toaccommodate the cone and duct in order that articles to be sprayed canbe received at the same level as other elements in the production line.

[0014] It is an object of the present invention to provide a colourspray apparatus in which powder colour can be changed quickly and easilyand which, moreover, is of relatively simple construction.

[0015] It is another object of the present invention to provide a powdercoating system in which both air borne and deposited overspray can berecovered by a system involving a small number of relatively simpleparts which are themselves readily cleaned.

[0016] It is a further object of the present invention to provide apowder spray booth in which the collection of deposited overspray isfacilitated whilst still balancing the extraction air flow along thelength of the booth.

[0017] It is a still further object of this invention to provide apowder spray booth of generally circular configuration which can beeasily incorporated in a production line and which is simple to clean.

[0018] The invention will now be summarised with respect to fourprincipal aspects: a diverter plate; sloped floor with cleaning air;pulsed cleaning air apparatus, and pulsed cleaning air method.

[0019] In one aspect the present invention provides a powder coatingsystem comprising a powder spray booth with walls and a floor having twoside portions and a downwardly offset region therebetween which definesa trough between the side portions, one or more powder spray devicespositioned with respect to the booth walls to spray articles passedthrough the booth via openings in the walls, a powder recovery systemhaving an overspray intake communicating with the interior of the booth,the powder recovery system including suction means for drawing overspraypowder from the booth interior via the overspray intake, and, a diverterplate held within the booth between the floor side portions such as toclose at least part of the trough and form a duct which is incommunication with the overspray intake, the diverter plate including atleast one aperture for the passage of overspray powder deposited thereonto the duct.

[0020] It has been found that with this apparatus it is possible to evenout air extraction to give balanced air flow in the booth whilst stillproviding an arrangement which is easy to clean particularly if, as ispreferred, the diverter plate is movable to a second raised positionallowing access to the trough. The provision of at least one apertureallows overspray powder deposited on the diverter plate to be drawntherethrough and into the powder recovery system.

[0021] Preferably the side portions are sloped down towards the diverterplate. The diverter plate may define a slot between it and each of theside portions.

[0022] Deposited overspray powder on the side portions will trickle downtowards the diverter plate and be extracted by the air flow to thepowder recovery system via the slots between the plate and the sideportions. As already noted, deposited overspray powder on the surface ofthe plate will be extracted via the apertures therein. As a consequencethe amount of deposited overspray powder in the booth at the start ofthe cleaning operation will be reduced so reducing the scale of thecleaning operation and consequently its duration.

[0023] The booth may have any desired configuration. It may have thecommon rectangular shape with the longitudinal axis running generallyhorizontally. Alternatively, the booth can be circular with the centralaxis running generally vertically. The provision of an air distributionduct in a circular booth formed by the diverter plate enables limitationof powder build up and optimisation of air distribution and velocitiesin the booth through control of the size and shape of the apertures inthe diverter plate. Advantage can therefore be taken of the easycleanability of circular booths without requiring that a special pit beprovided to position the booth in a production line. This is asignificant benefit as is the fact that operators can safely walk intothe booth which is not possible with known circular booths having aconical base.

[0024] In a rectangular booth, the overspray intake may be provided ator near one end of the booth with the diverter plate extending from thatend along part of the length of the booth. In a rectangular boothprovided with a plurality of automatic powder spray devices and havingslots in the side walls for the automatic powder spray devices, thelength of the diverter plate may be the distance between the end and thegun slot furthest from the end plus an offset. The offset can becomparatively small, a suitable value for a common booth design being200 mm.

[0025] It has been found that it is only necessary to provide thediverter plate in the part of the booth where automatic guns areemployed. This is because there are a higher number of guns in theautomatic gun portion of the booth and therefore more powder flow intothe booth there from the guns. Also, this part of the booth is closestto the extraction fan. Without the diverter plate, the fan can distortthe powder spray patterns from the guns and may draw the powder into thecollection system before it has a chance to adhere to the part. Theeffect of the diverter plate is to equalize the suction force of the fanso that powder has more time to adhere to the part and oversprayedpowder is drawn evenly towards the fan. In the manual gun section of thebooth, there are fewer guns and they are farther away from the fan, sothe patterns from those guns are not affected to such a great extent bythe fan. Therefore, the diverter plate is not as necessary in the manualgun section of the booth.

[0026] In a rectangular booth of the design shown in European PatentApplication No. 98940476.9 with an overspray intake at each end, adiverter plate may be provided extending from each end. It has beenfound that a booth with air intakes at both ends in fact produces thebest balancing of the air flow in the booth and actually results in a“dead” zone in the middle of the booth where powder coating isparticularly efficient since powder particles have an opportunity toadhere to the part relatively unaffected by the collection system airflows. The plates can be arranged to extend to either side of this“dead” zone.

[0027] In a particularly preferred embodiment, the diverter plate isformed in two or more sections, the diverter plate sections beingarranged at different vertical spacings from the bottom of the troughsuch that the duct has different heights along its length. It has befound with this arrangement it is possible to improve still further theair flow balance in the booth and to obtain more even suction.

[0028] In this embodiment, the plate section or sections adjacent the oreach overspray intake may have the greatest vertical spacing from thetrough bottom. With a rectangular booth having an overspray intake atone end, the sections may be arranged in a descending series of stepstowards the other end. With a circular booth having a centrally locatedoverspray intake, the section thereabove may be at maximum spacing withone or more lower sections on either side. The narrowing of the ductaway from the overspray intake produces the desired even suction andmore balanced air flow.

[0029] The diverter plate is suitably provided with a plurality ofapertures arranged in a pattern. With a rectangular booth, the patternmay be triangular with the apex being at the end of the booth closest tothe fan. This pattern has been found to give the best combination ofpowder collection and air balancing. The total hole cross-sectional areagradually increases from the end towards the middle of the booth.

[0030] The apertures in a preferred form are elongate in the lengthwisedirection of the plate to give maximum circumference for given crosssectional area and therefore maximum ability to draw deposited oversprayfrom the upper surface of the diverter plate.

[0031] In accordance with a second aspect, the present inventionprovides a powder coating system comprising a powder spray booth havingfloor and walls, one or more powder spray devices positioned withrespect to the walls to spray articles passed through the booth viaopenings in the walls, and a powder recovery system having an oversprayintake communicating with the interior of the booth, the powder recoverysystem including suction means for drawing overspray powder from thebooth interior via the overspray intake, wherein at least a portion ofthe booth floor is sloped and wherein cleaning air supply means isprovided for directing air down the sloped portion(s).

[0032] Whilst it has been known to make at least a portion of boothfloors sloping, the intended result of this, that deposited overspraypowder will eventually trickle down the sloped portion, does not alwaysoccur. There can be significant build ups of deposited overspray powderon the sloped portion or portions which adds to cleaning time and alsogives rise to danger of explosions. By providing a cleaning air supplywhich directs air down the sloped portion or portions, downward movementof deposited overspray powder is ensured to bring the depositedoverspray powder to a region where it can be easily cleaned, eithermanually or automatically by a mechanical scraper or the like and/orextraction in the exhaust air of the powder recovery system.

[0033] The cleaning air supply means may comprise a source of air and atleast one plenum extending along at least part of the sloped portion andlocated at the upper edge of the sloped portion, the plenum having atleast one air outlet, preferably plural air outlets.

[0034] Very preferably the air source provides periodically pulses ofair to the air outlets. It has been found that it is an unnecessarywaste of energy to constantly direct air across the slope portion orportions and it suffices just to pulse the air to start movement ofdeposited overspray powder down the sloped portion or portions. It iscurrently believed that the best effects are achieved when the cleaningair supply means directs the air generally parallel to the surface ofthe sloped portion or portions, preferably at an angle of 1-3° to thesloped portion or portions.

[0035] In the particularly preferred configuration of the first aspect,the cleaning air supply means of the second aspect may direct air downthe side portions along the length of the diverter panel.

[0036] In accordance with a third aspect, the present invention providesa powder spray system having a floor, and walls, one or more powderspray devices positioned with respect to the walls to spray articlespassed through the booth via openings in the walls, and a powderrecovery system having an overspray intake communicating with theinterior of the booth, the powder recovery system including suctionmeans for drawing overspray powder from the booth interior via theoverspray intake, wherein a cleaning air supply means is providedcomprising a source of air and at least one plenum with plural airoutlets, the air source providing pulses of air to the air outlets andthe plenum being arranged to direct the air pulses across an internalsurface of the booth on which overspray powder is deposited.

[0037] It has been found that pulses of air may be effective forcollection of deposited powder across any internal surface of the boothnot just sloped surfaces. The pulses of air cause the depositedoverspray powder to collect, either by falling in the case of theceiling or walls, or by movement along or across the booth in the caseof the floor and so facilitate extraction of the deposited overspraypowder by the powder recovery system. Good results are achieved withoutthe need for a constant air flow or a complicated structure fordirecting the air. Thus the system is very economical both as regardsmanufacture and operation.

[0038] The air source may be a compressed air source, one or more fansor an air supply of the powder recovery system. The former has theadvantage of cheapness whilst the latter makes for compactness andquietness since fans are relatively noisy.

[0039] Very preferably the first aspect is combined with the secondand/or third which results overall in a very significant reduction incleaning time coupled with even air distribution across the booth whichproduces higher transfer efficiency since the powder particles are givena greater opportunity to adhere to the part. These advantages areaccomplished while good powder containment within the booth is alsobeing achieved.

[0040] The invention also provides in a fourth aspect a method ofoperating a powder coating system including a powder spray booth havinga floor and walls, one or more powder spray devices and a powderrecovery system with an overspray inlet communicating with the interiorof the booth, the method comprising periodically directing jets of airacross an internal surface of the booth to collect deposited overspraypowder thereon.

[0041] The method thus involves providing air assist in the booth whichfacilitates collection and removal of deposited overspray powder.

[0042] The internal surface may be the floor and/or one or more wallsand/or the ceiling of the booth.

[0043] The jets of air are preferably directed sideways across thesurface, or lengthwise along the booth. In this way the powder isgathered together and easily collected by a cleaning operation along thebooth which may be either manual or automatic.

[0044] It has been found that good results are achieved when the airjets are pulsed on for five seconds for every five minutes of sprayingof articles in the booth. This prevents any significant build-up ofdeposited overspray powder by causing removal of the majority ofdeposited overspray from the booth with the result that the inventory ofpowder moving around in the system, particularly the quantity within thebooth itself, is kept to a minimum.

[0045] Alternatively or additionally the jets of air can be pulsed justprior to a colour change so that the amount of deposited powder whichhas to be removed during the cleaning operation is minimised.

[0046] Very preferably this fourth aspect is combined with the secondaspect and the air jets are directed across at least part of a slopingportion of the booth floor. For effective movement of depositedoverspray powder on the sloping portion(s), the air jets are directedgenerally parallel the sloping portion(s), preferably at an angle ofbetween 1-3° thereto.

[0047] The invention will now be further described by way of examplewith reference to the accompanying drawings in which:

[0048]FIG. 1 is a perspective view partly cut away of a powder boothforming part of a first embodiment of a powder coating system inaccordance with the invention;

[0049]FIG. 2 is a perspective view partly cut away of part of a powderspray booth forming part of a second embodiment of a powder coatingsystem in accordance with the invention;

[0050]FIG. 3 is a sectional detail of part of the booth of FIG. 2;

[0051]FIG. 3A is a sectional detail of an alternative embodiment of thebooth part of FIG. 3.

[0052]FIGS. 4 and 5 are plan views of a diverter plate for use in thespray booth of FIGS. 1 and 2;

[0053]FIG. 6 is an end view of the diverter plate of FIGS. 4 and 5;

[0054]FIG. 7 is a schematic side view of part of a third embodiment of apowder coating system in accordance with the invention;

[0055]FIG. 8 is a perspective view partly cut away of part of a powderspray booth forming part of the powder coating system of FIG. 7;

[0056]FIG. 9 is a schematic end view of a fourth embodiment of a powdercoating system in accordance with the invention;

[0057]FIG. 10 is a plan view of the powder coating system of FIG. 9;

[0058]FIG. 11 is a schematic plan view of a fifth embodiment of a powercoating system in accordance with the invention;

[0059]FIG. 12 is a section along X-X of the powder coating system ofFIG. 11;

[0060]FIG. 13 is a section along Y-Y of the powder coating system ofFIG. 11;

[0061]FIG. 14 is a schematic end view showing a cleaning system for usein the powder coating systems of FIGS. 9 to 13;

[0062]FIG. 15 is a schematic plan view showing the cleaning system ofFIG. 14;

[0063]FIG. 16 is a schematic end view showing an alternative cleaningsystem for use in the powder coating systems of FIGS. 9 to 13;

[0064]FIGS. 17 and 18 are plan views showing possible modificationswhich can be made to the powder coating booth of the powder coatingsystems of FIGS. 9 to 13;

[0065]FIG. 19 is a schematic view of a powder spray booth forming partof a further embodiment of a powder coating system in accordance withthe invention, and,

[0066]FIGS. 20 and 21 are schematic views of alternative powder spraybooths.

[0067]FIGS. 1 and 2 show a rectangular powder spray booth 2 with sidewalls 4, end walls 6 and a floor 10. The booth 2 further has a conveyor(not shown) from which objects are suspended and conveyed through thebooth 2 via openings 12 in the end walls 6 for coating with powder by anumber of spray devices (also not shown). The booth 2 shown in FIGS. 1and 2 has a slot 14 for an automatic spray device and an opening 16 toallow use of a manually operated spray device in each side wall. Howeverit will be appreciated that the number and position of spray devices canbe varied depending on the objects to be coated.

[0068] The ceiling, walls 4, 6 and floor 10 of the booth 2 arepreferably made from a non-conducting material such as plastic. By usingplastic, the powder sprayed by the spray devices if electrostaticallycharged will have a reduced tendency to adhere to the ceiling and walls4, 6 since it will not be electrostatically attracted to the walls 4, 6and ceiling and instead will fall under gravity and collect on the floor10 of the booth 2. For durability the floor 10 or at least the part orparts on which an operator will walk may instead be made of stainlesssteel.

[0069] The booth 2 will be provided with a powder recovery system whichmay include filters and/or one or more cyclone separators as furtherdescribed below with respect to other embodiments of the powder coatingsystem. Whatever form the powder recovery system takes, there will be anoverspray intake communicating with the interior of the booth 2 andproviding a current of exhaust air within the booth and into theoverspray intake. The current of exhaust air will serve to extractairborne overspray powder. The skilled man can readily choose a suitablepowder recovery system from those known in the art.

[0070] As rectangular powder spray booths are preferably cleaned fromone end to the other, for the purposes of cleaning the overspray intakeis preferably located at one end of the booth. In the booth depicted inFIGS. 1 and 2, the overspray intake is shown in dotted outline at 18 andis located at one corner of the booth. Rising thereabove is a duct 20which leads to the powder recovery system which is preferably a powderrecovery system of the type styled “close coupled cyclone” as describedin European Patent Application No. 94929600.8, now European Patent No.723,481.

[0071] The floor 10 of the booth 2 shown in FIGS. 1 and 2 includes twosloping portions 22 on either side thereof, the sloping portions 22being spaced and the remainder of the floor 10 being offset therefrom todefine a trough 24 between the sloping portions 22. The wall of thetrough 24 is cut away at the end of the booth 2 where the oversprayintake 18 is located to provide a connection between the oversprayintake 18 and the trough 24 and hence the rest of the interior of thebooth 2.

[0072] A diverter plate 26 is positioned in the trough 24 at the endwhere the overspray intake 18 is located and extends from that end. Thelength of the diverter plate 26 is preferably equal to the distance fromthe end of the booth 2 to the centre line of the automatic spray deviceslot 14 which is furthest from that end plus an offset. The offset maysuitably be of the order of 200 mm. The plate 26 is suitably spaced fromthe side portions 22 to define slots 27 therebetween.

[0073] The plate 26 has a pattern of holes 28 therein. Two possiblepatterns are shown in FIGS. 4 and 5. Both are triangular with the apexbeing at the end of the booth 2 where the overspray intake 18 islocated. The holes 28 are elongate in the lengthwise direction of theplate 26 and hence the booth 2. As illustrated in FIG. 6 the plate 26has an upper surface which is slightly peaked for strength andstiffness.

[0074] The diverter plate 26 is supported by tabs 29 in the positionshown in FIGS. 1 and 2 but is mounted to the end wall 6 via hinges 30 toallow it to be pivoted up and against the end wall 6. The portion ofduct 20 extending above the side floor portions 22 is separated from theinterior of the booth 2 by two doors 32 each of which is also mounted byhinges 33 so that the doors 32 can also be pivoted away against the endwall 6 allowing access to the interior of the duct 20.

[0075] The booth 2 shown in FIG. 2 differs from that of FIG. 1 in that aplenum 34 is provided at the upper edge of each of the side portions 22.The plenum 34 on the left-hand of the booth in the sense of the Figuresis shown in greater detail in the sectional view of FIG. 3. The plenum34 comprises a tube mounted within the wall 4 and formed with spacedoutlets 35 along the length thereof. The plenum 34 is connected to asource of pressurised air via a valve shown schematically at 36 and 37,respectively, in FIG. 2. Air from the source 36 is directed out of theair outlets 35 as jets across the side portions 22.

[0076]FIG. 3A shows an alternative arrangement for providing pulsed airflow across the side portions 22. The arrangement has a number offeatures in common with that illustrated in FIG. 3 and where appropriatelike reference numerals will be used for like parts.

[0077] In the arrangement of FIG. 3A, a plenum 34 again extends thelength of the side portion at its upper edge. The plenum is formed intwo parts 34 a, 34 b, the forwardmost part 34 b being formed with spacedoutlets 35 which extend to a generally v-shaped groove 38 which ismilled in the forwardmost part 34 b.

[0078] The plenum is supplied by a series of air feed tubes 39 spacedalong the length of the booth. The feed tubes 39 are in turn supplied bya valved pressurised air source as in the arrangement of FIG. 3 but notshown in FIG. 3A, the connections being via threaded inlet fittings 40.

[0079] Whichever arrangement is employed, that of FIG. 3 or that of FIG.3A, the air outlets 35 are preferably arranged to direct the air jets atan angle of 1-3° to the side portions 22. Therefore if the angle (a) ofthe side portions 22 is 37 o with respect to the horizontal floor of thebooth, the air outlets 35 will direct air at an angle (b) of 38-40° tothe horizontal. This orientation of air outlets 35 will cause the airjets to impinge on side portion 22 at an angle of 1 degree to 3 degrees.In the arrangement of FIG. 3A where the groove 38 is provided, the lowerwall of the groove may be at an angle (c) of 135° to the vertical, thatis, 45° to the horizontal.

[0080] The plenum 34 of the arrangement shown in FIG. 3 may be a PVCextrusion which is bonded to the inner panel 41 of wall 4.Alternatively, as is illustrated by FIG. 3A, the plenum can be attachedexternally of the wall 4. The plenum 34 can also take other forms fromthose illustrated in FIGS. 3 and 3A.

[0081] In use, the booth 2 is employed to spray powder on to objectspassing therethrough either from automatic guns extending through theslots 14 and/or by manual guns directed through the openings 16. Airborne overspray powder is extracted from the interior of the booth 2 onthe current of exhaust air produced by the powder recovery system viathe overspray extract 18 and duct 20. Overspray powder which falls outof the transport air provided by the powder recovery system will bedeposited on the floor 10 of the booth 2 and so on the side portions 22,the bottom of the trough 24 and the plate 26. The flow of exhaust aircaused by the air recovery module along the trough 24 will tend to drawdeposited overspray powder on the upper surface of the diverter plate 26down into the trough 24 therebelow either through the holes 28 or theslots 27 between the side portions 22 and the diverter plate 26. It hasbeen found that the elongate shape of the holes 28 maximises the areatherearound from which deposited overspray powder is drawn into theholes 28 and thence to the overspray intake 18 on the current of exhaustair. The peaking of the upper surface 29 of the plate 26 assists thepassage of deposited overspray powder not drawn through the holes 28into the slots 27 and so again to the overspray intake 18.

[0082] Deposited overspray powder on the side portions 22 will to anextent by gravity naturally trickle down the side portions due to theirsloping and into the trough 24 and so into the current of exhaust airproduced by the powder recovery system. The booth 2 of FIG. 2 howeverprovides an air assist to this process through the plenums 34. The jetsof air produced from the air outlets 35 of the plenums 34 increase themovement of the deposited overspray powder down the side portions 22.With short runs between colour changes, an air pulse may be providedjust prior to the colour change. With longer runs, an air pulse isprovided periodically to prevent deposited overspray powder build-up andso reduce the inventory of powder within the system, particularly theamount of powder in the booth 2. Whilst the air assist could be providedconstantly, it has been found that in fact suffices to provide periodicpulses of air to set in motion the deposited overspray powder on theside portions 22. In one successful experiment, a pulse of five secondsevery five minutes served to keep the side portions 22 reasonably clearof deposited overspray powder. Pulsing the air, as opposed to constantlysupplying compressed air, reduces system energy costs.

[0083] The air assist provided by the plenums 34 not only helps keep theside portions 22 clear but also increases the collection of depositedoverspray powder on the upper surface from the diverter plate 26.

[0084] The great majority of deposited overspray powder which iscollected off the side portions 22 and the diverter plate 26 isre-entrained in the exhaust air flow of the powder recovery system andso extracted as, in effect, air borne overspray powder from the booth 2.

[0085] The diverter panel 26 could extend the full length of the booth2. However it has been found that it suffices for it to extend just pastthe slots 14 for automatic guns by an offset which, as noted above, canbe in the order of 200 mm. This is because the higher number of guns inthe automatic gun portion of the booth produces more powder flow, andthis greater powder flow is closer to the fan than the manual guns. Theeffect of the diverter plate is to equalize the suction force of the fanso that the powder has more time to adhere to the part and oversprayedpowder is more evenly drawn into the collection system. Since the manualguns are farther from the fan, their spray patterns are not as greatlyaffected by the fan and the need for the diverter plate is thereforereduced with respect to those guns.

[0086] The diverter plate 26 functions to even out air distributionalong the booth 2 to give an air balance in the powder booth which leadsto higher transfer efficiency while ensuring good powder containment.Thus it serves to reduce the amount of deposited overspray powder and soincrease the amount of air borne overspray powder. This balancing effectis achieved in part by the pattern of holes 28. As the diverter plate 26is an air flow restrictor, the size, number and pattern of the holesdetermines the air velocity through the overspray intake 18. As anexample, the diverter plate 26 may be arranged so that in combinationwith the input air velocity of the powder recovery system and the cubicfeet per meter rating of the booth 2, the air velocity through theoverspray intake 18 is 2000 ft/min.

[0087] The booth 2 shown in FIGS. 1 and 2 has a single diverter plate 26which is used in conjunction with the single overspray intake 18.However in a booth with two overspray intakes such as that shown inEuropean Patent Application No. 98940476.9, a diverter plate 26 could beprovided at both ends extending towards the middle of the booth 2. Thediverter plates 26 would preferably stop short of the “dead” zone in themiddle of the booth which it has been found is created by the provisionof two overspray intakes, one at each end of the booth. The dead zone isa relatively quiet area of the booth, in that the air flows caused bythe collection system are not as strong in that area of the booth as inthe remainder of the booth.

[0088] During spraying, air is periodically supplied to the plenums 34to produce air jets down the side portions 22 and so cause movement ofdeposited overspray powder thereon into the trough 24 and on to thediverter plate 26. The air jets will also assist in keeping the diverterplate 26 clean. In one working embodiment, the plenums 35 had 0.5 mmdiameter holes set at a 15 mm spacing and powder collection was achievedby blowing air at 4 bar pressure for five seconds every five minutes. Aswill be appreciated, the air assist parameters given for any given boothwill depend on various parameters such as the type of powder coatingmaterial, the configuration on the booth, and in particular, the angleof sloping of the side portions 22. The provision of air assist meansthat if desired the angle of sloping can be reduced which makes iteasier for operators to move around within the booth 2 and facilitatesconstruction of the booth 2.

[0089]FIGS. 7 and 8 illustrates schematically a further embodiment whichhas many features in common with those of FIGS. 1 and 2 and thereforelike reference numerals will be used for like parts. In the embodimentshown in FIGS. 7 and 8, the diverter plate 26 extends the length of thebooth which is provided at one end with a powder recovery system havinga cyclone separator 42. The plate 26 need not extend the full length ofthe booth and could instead stop short of the end distant from thepowder recovery system like the plate 26 of the powder spray systemsillustrated in FIGS. 1 and 2. However, unlike those systems, the plate26 is formed in a plurality of sections 44 each of which may beconsidered as a separate diverter plate, the plural sections beingarranged as a series of steps descending away from the powder recoverysystem. The sections 44 may be integral or separate. As illustrated inFIG. 8 they may be arranged such that a slot 46 is provided between eachsection 44 and the next section down the booth.

[0090] The advantage in embodiments illustrated in FIGS. 7 and 8 is thatit has been found to give even more balanced airflow throughout thebooth because of the narrowing powder suction duct below the diverterplate 26 as the diverter plate sections 44 step down in the directionaway from the cyclone separator 42. In addition, the diverter platesections 44 are kept almost free of powder due to the airflow strikingtheir surfaces in an almost parallel manner and drawing powder throughthe slots 46 formed between the plate sections 44.

[0091] Whilst rectangular booths as shown in FIGS. 1, 2 and 7 are verycommon, it is also known to use cylindrical or circular booths. Withmany known circular booths there is a problem which is that, foreffective overspray powder extraction, it has been found necessary toprovide a conical floor. In order to accommodate the conical floor thebooth has either to be very tall or, in order that articles may bereceived at the same level as at other stations of a conveyor line, apit has to be provided for the conical floor.

[0092] It has now been found that it is possible to obtain goodoverspray powder recovery with a circular booth having a flat base byincorporating therein a diverter plate and using this in conjunctionwith a powder recovery system which exhausts air from the booth.

[0093]FIGS. 9 and 10 illustrate a circular booth 2 with a centrallylocated overspray intake leading via a duct 20 to a cyclone separator42. A diverter plate 26 extends diametrically across the booth 2 belowthe path taken by articles to be sprayed which enter and leave viaopenings which may be closed by doors 48. On either side of the plate26, the booth floor 10 slopes upwards towards the booth wall 4 in eachside of which three slots 14 are provided for automatic guns shownschematically at 50 together with the gun mounts shown schematically at52. As in the embodiment of FIGS. 1 and 2, the diverter plate 26 may behinged along one edge so that it can be raised up to the side forcleaning of the trough 24, as is illustrated in dot-dash lines in FIG.9.

[0094] The circular booth 2 has a low height and so no pit or platformis required. An operator can easily walk into the booth 2 so that it canbe cleaned of any residual powder when changing colours by wiping. Thereis no safety issue as in current commercial booths since the operatorcannot fall into a deep conical floor as there is none.

[0095] FIGS. 11 to 13 illustrate a circular booth 2 where a central,diametrically extending, diverter plate 26 is arranged in steppedfashion similarly to the embodiment illustrated in FIGS. 7 and 8. Thediverter plate 26 is formed in three sections 44, the two side sectionsbeing lower than the central section which is above the extractionpoint. The result again is balanced air flow through the booth 2 andeven suction across the booth base because the duct 24 is narrowest inthe regions most remote from the extraction point.

[0096] As can be seen in FIG. 11, the diverter plate sections 44 may beslightly peaked which, as noted above with respect of FIG. 6, enhancesstrength and stiffness. FIG. 11 also shows that the diverter platesections 44 may be hinged to one of the side portions 22 to allow themto be moved up to the position shown in dotted outline and thereby giveaccess to the trough 24 which extends through the booth.

[0097] The circular booths 2 of FIGS. 9 to 13 can be manually cleanedsuch as by blowing them down with an air wand or wiping. Alternatively,automatic cleaning devices could be used. FIGS. 14 and 15 illustrate anautomatic cleaning arrangement with a double “D” profile cleaning airring 54 shown in both an upper position and a lower position. The ring54 directs air towards the walls 4 of the booth 2 as it is lowered andraised therein. As cleaning ring 54 is lowered from the ceiling, itblows any powder which has collected on the walls down the walls of thebooth and into the collection system housed in the lower portion of thebooth. The ring 54 may be retracted into the booth roof for normalcleaning.

[0098]FIG. 16 illustrates an alternative system for automatic cleaningwhich comprises an air cleaning frame 56 which rotates inside the booth2 whilst blowing air onto the walls 4 and floor 10 to remove depositedoverspray powder which is collected through the trough in the bottom ofthe booth. The cleaning frame 56 could be partial as illustrated orcould be double-sided or mirrored to speed cleaning. The frame 56 wouldpreferably be parked outside the booth 2 when the booth is in normaloperation. To clean the booth 2, the frame 56 would be attached to theconveyor and moved into the booth 2.

[0099] In order to allow manual powder coating guns to be used incombination with automatic powder spray guns, the circular configurationshown in FIGS. 9 to 16 may be modified to provide at least one stationfor an operator. FIGS. 17 and 18 illustrate modified booth shapes whichaccommodate manual spray guns. The illustrated configurations allowmanual spray guns to be used from both sides of the booth 2 but manualguns used from one side alone may suffice in which case the other sidewould preferably be smoothly curved to prevent accumulation of powdertherein. It will be appreciated that other shapes are possible; Forexample, rather than being indented as shown in FIG. 18 the booth wallsmay be straight between the sides of the article entrance slot 12 andthe automatic gun slots 14.

[0100] All of the circular booths embodiments may be provided with airassisted overspray collection by fitting plenums to direct air jets downthe floor side portions 22 and so cause movement of deposited overspraythereon into the trough 24 and onto the diverter plate 26. As with therectangular booth embodiments, the provision of air assist will meanthat the sloping of the side portions 22 may be reduced which will makeit easier for operators to move around within the booth 2 and facilitateits construction.

[0101] The air assist need not be used in conjunction with a diverterplate 26. FIGS. 19 to 21 illustrate arrangements in which air assist isemployed simply in combination with a sloped floor portion. In thearrangement of FIG. 19 nearly the whole of the floor 10 is sloped andthe air assist is provided across the complete upper edge of the slopedfloor 10. This Figure also serves to show schematically the withdrawalof air borne overspray powder via duct 20 and into a cyclone separator42 of a powder recovery system.

[0102] In a circular booth, the whole of the booth floor 10 may besloped. This is illustrated in FIG. 20 which shows a circular booth 2having a sloped floor 10. As also illustrated the floor may beperforated and formed in three sections with the outer sections beinghinged or otherwise raisable to facilitate cleaning. In the FIG. 20embodiment, the center section of the diverter plate would remainstationery and the outer two sections could be hinged upwardly to allowthe operator to enter from either side of the booth.

[0103]FIG. 21 shows a further alternative in which the floor 10 has atriangular cross-section and the air assist is provided at the apexthereof. As shown by the arrows, the air assist moves depositedoverspray powder down each side of the floor 10 to prevent build-up onthe floor 10 and to collect the deposited overspray at the sides of thebooth 2. The booth 2 may have side inlet ducts for receiving thecollected overspray powder and directing it to the powder recoverysystem.

[0104] In still further alternatives, the air assist is provided acrossother non-sloped internal surfaces of the booth 2, for example, one ormore of the walls or the ceiling. Air assist can also be provided to anadvantage with a non-sloped floor. A particular embodiment which mayhave great utility is to provide air assist centrally of the boothdisclosed in European Patent Application No. 98940476.9 such that thejets of air are directed towards the ends of the booth and thus to eachof the overspray intakes provided at those ends. The air assist willfacilitate collection of deposited overspray powder on the floor andmovement thereof towards the overspray intakes for recovery by thepowder recovery system.

[0105] In all these alternatives, the air assist may be continuous orpulsed. The latter has the advantage of economy due to reduced energyrequirements for the air source and therefore cost savings.

[0106] With a long run between the colour powder changes, it isdesirable that an air pulse be provided periodically, whilst with shortruns, it can suffice to provide a pulse just prior to the colour change.

[0107] Reverting to FIGS. 1 and 2, the cleaning operation which isperformed when the colour of the powder is to be changed will now bedescribed. It will be appreciated that the description applies equallyto the other embodiments provided with a diverter plate 26 and a powderrecovery system which provides for air exhaust. The powder spray devicesare shut off and doors closed across the access openings 12 in the endwall 6. The diverter panel 26 is pivoted up against the adjacent endwall 6 as too are the doors 32 to the duct 20. An operator preferablyusing an air hose, begins at the opposite end of the booth 2 from theduct 20 and moves along the booth blowing the deposited overspray powderwhich remains therein from all wall and floor surfaces and the surfacesof the diverter panel 26, the duct 20 and the overspray intake 18. Theselast two operations are simplified because of the hinged mounting of thediverter panel 26 and the doors 32 of the duct 20. As the powder isblown off of the surfaces of the booth, it is drawn into the extractionduct 20 by the fan.

[0108] The amount of deposited overspray powder which has to be removedin this operation is much less than with known booths because asignificant proportion of the deposited overspray powder will havealready been removed due to the action of the diverter plate 26, slopedside portions 22 and the air plenums 34. Consequently the amount ofrecycling work to be done during the cleaning process is reduced whichreduces labour costs. Also, in some prior systems, powder has to becollected in a dust pan or waste container and thrown away becauserecycling has not been completed by the time the cleaning process isover. This waste of powder coating material will not occur in thepresent system due to the reduced time and effort required to clean thebooth.

[0109] In tests with this booth, it has been found to be possible toreduce booth cleaning time to below fifteen minutes.

[0110] These improvements in colour change capability are achievedwhilst at the same time improving the actual performance of the boothsince the diverter plate 26 acts to even out, or balance across thelength of the booth the air flows which draw oversprayed powder into thesystem. This has the effect of improving the transfer efficiency of theguns because the powder particles have a better opportunity to attach tothe part being coated. In addition, oversprayed powder is moreeffectively contained within the booth by mans of this design.

1. A powder coating system comprising a powder spray booth with wallsand floor having two side portions and a downwardly offset regiontherebetween which defines a trough between the side portions, one ormore powder spray devices positioned with respect to the booth walls tospray articles passed through the booth via openings in the end walls, apowder recovery system having an overspray intake communicating with theinterior of the booth, the powder recovery system including suctionmeans for drawing overspray powder from the booth interior into theoverspray intake, and, a diverter plate held within the booth betweenthe floor side portions such as to close at least part of the trough andform a duct in communication with the overspray intake, the diverterplate including at least one aperture for the passage of overspraypowder deposited thereon to the duct.
 2. A powder coating systemcomprising a powder spray booth having walls and a floor, one or morepowder spray devices positioned with respect to the walls to sprayarticles passed through the booth via openings in the walls, and apowder recovery system having an overspray intake communicating with theinterior of the booth, the powder recovery system including suctionmeans for drawing overspray powder from the booth interior into theoverspray intake, wherein at least a portion of the booth floor issloped and wherein cleaning air supply means is provided for directingair down the sloped portion(s).
 3. A powder spray system comprising apowder spray booth having walls and, one or more powder spray devicespositioned with respect to the walls to spray articles passed throughthe booth via openings in the walls, and a powder recovery system havingan overspray intake communicating with the interior of the booth, thepowder recovery system including suction means for drawing overspraypowder from the booth interior into the overspray intake, whereincleaning air supply means is provided comprising a source of air and atleast one plenum with at least one air outlet, the air source providingpulses of air to the air outlets and the plenum being arranged to directthe air pulses across an internal surface of the booth on whichoverspray powder is deposited.
 4. A powder spray system as claimed inclaim 3 wherein the floor and/or one or more of the walls and/or aceiling of the spray booth is provided with a plenum.
 5. A powdercoating system as claimed in any one of claims 2 to 4 the booth floorhaving two side portions and a downwardly offset region therebetweenwhich defines a trough between the side portions and the apparatusfurther comprising a diverter plate held within the booth between thefloor side portions such as to close at least part of the trough andform a duct in communication with the overspray intake, the diverterplate including at least one aperture for the passage of overspraypowder deposited thereon to the duct.
 6. A powder coating system asclaimed in either claim 1 or claim 5 wherein the booth is generallyrectangular in shape and the overspray intake is provided at or near oneor both ends of the booth and wherein the diverter plate extends fromthe or each end along part of the length of the booth.
 7. A powdercoating system as claimed in claim 6 wherein there are a plurality ofautomatic powder spray devices and the side walls include slots for theautomatic powder spray devices and wherein the length of diverter plateis the distance between the end and the gun slot furthest from the endplus an offset.
 8. A powder coating system as claimed in any one ofclaims 1 or 5 to 7 wherein the diverter plate is provided with aplurality of apertures arranged in a pattern.
 9. A powder coating systemas claimed in claim 8 when dependent on either claim 6 or claim 7wherein the pattern is triangular, the apex being at the booth end. 10.A powder coating system as claimed in either claim 8 or claim 9 whereinthe plate is generally rectangular in shape and the apertures areelongate in the lengthwise direction of the plate.
 11. A powder coatingsystem as claimed in any one of claims 1 or 5 to 10 wherein the diverterplate is mounted to be movable between the position between the sideportions and a second position.
 12. A powder coating system as claimedin any one of claims 1 or 5 to 11 wherein the diverter plate is mountedbetween the bottom edges of the side portions such as to define a slotbetween it and each of the side portions.
 13. A powder coating system asclaimed in any one of claims 1 to 5 or 11 wherein the diverter platecomprises two or more sections arranged at different vertical spacingsfrom the bottom of the trough such that the duct has different heightsalong its length.
 14. A powder coating system as claimed in claim 13wherein the plate section(s) closest to the overspray intake(s) has thegreatest vertical spacing from the trough bottom.
 15. A powder coatingsystem as claimed in any one of claims 1 or 5 to 14 wherein at least oneof the side portions slopes downwardly towards the diverter plate.
 16. Apowder coating system as claimed in claim 15 as dependent on claim 5 orany one of claims 6 to 14 when dependent on claim 5 wherein the cleaningair supply means directs air down the side portions along the length ofthe diverter plate.
 17. A powder coating system as claimed in any one ofclaim 2 or claims 5 to 16 when dependent on claim 2 wherein the cleaningair supply means comprises a source of air and at least one plenum withplural air outlets extending along at least part of the sloped portionand located at the upper edge of the sloped portion.
 18. A powdercoating system as claimed in claim 17 wherein the outlets directs theair at an angle of 1-3° to the sloped portion.
 19. A powder coatingsystem as claimed in either claim 17 or claim 18 wherein the air sourceprovides periodic pulses of air to the air outlets.
 20. A powder coatingsystem as claimed in any one of claims 3, 4 or 17 to 19 wherein the airsource is a compressed air source, one or more fans or an air supply ofthe powder recovery system.
 21. A powder coating system as claimed inany one of claims 1 to 5 or 8 to 20 as dependent on any one of claims 1to 5 wherein the booth has a rectangular or circular cross-section. 22.A method of operating a powder coating system including a powder spraybooth having walls and a floor, one or more powder spray devices and apowder recovery system with an overspray inlet communicating with theinterior of the booth, the method comprising periodically directing jetsof air across an internal surface of the booth to collect depositedoverspray powder thereon.
 23. A method as claimed in claim 22 whereinthe jets of air are directed either sideways across the booth internalsurface or, with a rectangular booth, lengthwise along the booth.
 24. Amethod as claimed in either claim 22 or claim 23 wherein at least aportion of the booth floor is sloped and wherein the air jets aredirected across at least part of the sloping portion(s).
 25. A method asclaimed in claim 24 wherein the air jets are directed at an angle ofbetween 1-3° to the sloping portions.
 26. A method as claimed in any oneof claims 22 to 25 wherein the air jets are pulsed on for five secondsevery five minutes of spraying of articles in the booth.
 27. A method asclaimed in any one of claims 22 to 26 wherein the air jets are pulsed onjust prior to a change of powder colour.